At present many transition metal complexes have been used as catalysts for organic synthetic reactions. It is well known that the ligand plays a very important role, together with the transition metals as the central metals, as a factor to make full use of the performance or activity of those catalysts. Many phosphine compounds, for example, have been developed as the ligands and have had a key role as such.
The most important thing is to constitute an optimal catalyst for each of the various kinds of reactions and substrates. However, the combination of the central metal and the phosphine ligand, constituting the catalyst, is so complex that the known phosphine ligands may, in some cases, be insufficient without, for example, yielding enough catalytic activity for use in the practical industrial production. Thus, development of excellent novel phosphine ligands is still eagerly desired.